Radar transceivers operating at millimeter wavelengths have been in use for some time on vehicles, where they are installed to provide such features as warnings of obstacles that may not be visible to a driver of the vehicle, or for autonomous cruise control (ACC). Because of their use in vehicles, the transceivers have to comply with a number of constraints, which taken together make it extremely difficult to implement a simple, efficient transceiver that is to be usable in a mass market environment.
Some of the constraints are inherent to operating with millimeter waves, which are typically transmitted in waveguides, microstrips, or by short wire bonds between components. The problems generated by the millimeter (mm) wavelengths include requirements for close tolerances for mm wave structures such as the waveguides, microstrip chip adhesion, and wire bonds. Failure to meet these requirements leads to unwanted reflections, cross talk between adjacent components, and/or absorption in the transceiver, with consequent degradation of received or transmitted signals. Typical cross-talk in adjacent mm wave receivers can be of the order of 15 dB or more.
Other constraints arise from the need to use the transceiver in a vehicle. Vehicular use requires that the transceiver be mechanically and electrically robust, be able to operate as an all-weather system, be relatively simple to construct, and preferably be relatively simple to maintain. The latter constraints are necessary in order to keep the cost of the transceiver to acceptable levels. The former constraints must be met so that the transceiver continues to function in the vehicle.
In an article titled “A Compact Manufacturable 76–77-GHz Radar Module for Commercial ACC Applications,” by Gresham et al., in IEEE Transactions on Microwave Theory and Techniques, 49 (2001), the authors describe a transceiver module for a pulsed Doppler application. The module is switched between transmitting and receiving modes. In the receiving mode, the module operates, inter alia, a mixer which mixes received 76–77 GHz signals with local oscillator 76–77 GHz signals.
Modem vehicular radars typically require implementation of a multi-channel architecture. This leads to a complex multi-function front end. The complexity and stringent requirements on the transceiver lead to high cost solutions which limit the applicability of the technology.
There is thus a need for a low-cost, simple system for vehicular radar.